Abstract
Addition of yttrium to nickel-base alloys is known to improve their oxidation resistance. It is not clear, however, if a comparable effect is expected by addition of yttria or not. This question was investigated by comparing a hot corrosion behavior in a crucible and cyclic oxidation behavior in oxygen gas of a yttria added alloy with those of its yttria-free control of the same composition. As for the hot-corrosion, addition of yttria caused no significant difference for the solution-treated specimens, while it increased corrosion susceptibility for the as-extruded ones. The increase was considered to be due to a smaller crystal-grain size for the yttria-added specimen. Addition of yttria increased corrosion susceptibility to the dry oxidation as well. The reason was less clear. A possible one was a fine scale structure caused by yttria addition, which might have prevented formation of protective alumina layer over the alloy surface.
